The ordinary twist drill and the ordinary spade drill has two cutting edges disposed generally radial of one another and connected by a web. This wed is necessary in order to grind and sharpen the cutting edges of the drill.
The ordinary twist drill and the ordinary spade drill will drill a hole in a stack or layer of two or more plates, however, the web does cause resistance to drilling because at the web area no cutting can occur because there is due to its location on the drill axis cuts a minimal amount.
The newer metal cutting drills or hole mills which are designed to use each manufacturer's special design inserts will not drill a hole in a stack or layer of plates two or more because they do not cut through center on center. This design of drill develops a conical shaped where the drill exits the first part layer, this conical shaped disc then revolves with the drill making it impossible to cut this conical shaped disc into chips so that they may exit the cut. With the advancement of the drill feed and with rotation of the drill the only thing that can happen is for the drill to fail.